What Is MPG and MPGe? Fuel Economy Units Explained

MPG is the number of miles a vehicle travels on one gallon of fuel. MPGe, “miles per gallon of gasoline-equivalent,” is the number of miles a vehicle travels on an amount of energy equal to the energy in one gallon of gasoline. MPG fits vehicles that burn liquid fuel. MPGe exists so that vehicles that run on electricity, such as battery-electric cars and plug-in hybrids in electric mode, can sit on the same scale as gasoline cars.

Key takeaways

• A higher MPG or MPGe means the vehicle goes farther on the same amount of energy.
• EPA defines the energy in one gallon of gasoline as equal to 33.7 kilowatt-hours (kWh) of electricity, and that is the bridge behind every MPGe figure.
• MPGe compares energy use, not cost. What you pay depends on local electricity and gasoline prices.
• MPG is not linear: the same MPG gain saves a lot of fuel at low MPG and little at high MPG.

What MPG measures

On the EPA fuel economy label, MPG appears as city, highway and combined values for gasoline, diesel and conventional hybrid vehicles. Combined is the large number on the label and is built from city and highway results; see city vs highway MPG and the combined rating. The numbers come from standardized laboratory tests rather than from a single road trip, a process explained in how the EPA tests fuel economy.

What MPGe measures

An electric vehicle does not use gallons, so the EPA converts. According to the EPA, a gallon of gasoline has the energy equivalent of 33.7 kWh of electricity. A vehicle that uses 33.7 kWh to drive 100 miles uses the energy of one gallon over that distance, so its rating is 100 MPGe. The EPA’s electric vehicle label defines MPGe as the number of miles the vehicle can go using a quantity of fuel with the same energy content as a gallon of gasoline.

EPA’s MPGe values include charging losses and assume Level 2, alternating-current charging, so they reflect energy drawn from the wall rather than energy reaching the battery. The label also shows kWh per 100 miles, which is the more direct measure of electricity use. See kWh per 100 miles and EV efficiency.

Where you will see each unit

Vehicle type	Units on the EPA label
Gasoline, diesel, conventional hybrid	MPG (city, highway, combined)
Battery-electric	MPGe, plus kWh per 100 miles and range
Plug-in hybrid	MPGe on electricity, MPG on gasoline, plus kWh per 100 miles

The plug-in hybrid label shows two boxes: the left-hand box gives fuel economy on electricity in MPGe, and the right-hand box gives fuel economy in MPG once the battery is emptied and the vehicle runs on gasoline. How those are combined is covered in how plug-in hybrids are rated.

Why MPG can mislead

MPG puts distance on top and fuel on the bottom, so equal MPG steps are not equal fuel savings. Fuel used over a set distance is what actually leaves your tank, and it is the reciprocal of MPG. For 15,000 miles of driving, the same distance the EPA label assumes:

MPG	Gallons used in 15,000 miles
15	1,000
20	750
25	600
30	500
40	375
50	300

Going from 15 to 20 MPG cuts 250 gallons. Going from 40 to 50 MPG, a bigger gain on paper at twice the size, cuts only 75 gallons. This is why EPA labels now also show consumption, in gallons per 100 miles for liquid fuels and kWh per 100 miles for electricity. The label’s own wording is that consumption allows more accurate energy-usage comparisons between vehicles.

What MPGe does not tell you

• Cost. One kWh and one gallon cost different amounts, and both prices move. MPGe cannot rank vehicles by dollars; use a cost calculation such as the fuel cost calculator or the EV vs gas calculator.
• Range. MPGe says how much energy a mile takes, not how far a full battery goes. See EV range explained.
• Your own result. Labels are for comparing vehicles under identical conditions, a point developed in real-world MPG vs the EPA label.

Converting to other units

Hydrogen fuel cell vehicles are rated in MPGe too; see hydrogen fuel cell vehicles basics. If you prefer liters per 100 kilometers or kilometers per liter, the conversions are plain arithmetic. See MPG to L/100 km and other conversions or use the MPG converter.